For connecting methods of two parts, several methods such as a method using a connecting part, a method arranging an excessive portion to connecting intent parts to connect them, and welding method are generally known. These methods have several drawbacks, including increased costs caused by an increased number of parts, increased size caused by adding excessive portions, and deformation of the parts caused by heating.
To achieve easier connecting, a connecting method has been disclosed in JP2002-364622A2. In this document, an attaching member is connected to an attachment base. The attaching member includes a ring-shaped ditch arranged at one side of the attaching member which faces to the attachment base. The distance between both inner walls of the ring-shaped ditch becomes close with the position moved from a bottom to an opening. The attachment base includes a ring-shaped projecting portion corresponding to the ring-shaped ditch.
When the attaching member is connected to the attachment base, the ring-shaped projecting portion is inserted into the ring-shaped ditch, and the ring-shaped projecting portion is plastically deformed by compression force. Then, the attaching member and the attachment base are rigidly connected.
According to this configuration, the thickness of the ring-shaped projecting portion cannot be thick since it has to plastically deform. Therefore, it is difficult to apply the connecting system to parts which have to be connected to each other with high strength. In addition, the ring-shaped projecting portion has an inclined portion at the edge portion to make it easy to deform. In this case, the edge portion of the ring-shaped projecting portion has to be shaped thin. It makes the manufacturing process complicated and the connecting strength is reduced.